Multiphoton curing to provide encapsulated optical elements

ABSTRACT

Methods of fabricating optical elements that are encapsulated in monolithic matrices. The present invention is based, at least in one aspect, upon the concept of using multiphoton, multi-step photocuring to fabricate encapsulated optical element(s) within a body of a photopolymerizable composition. Imagewise, multi-photon polymerization techniques are used to form the optical element. The body surrounding the optical element is also photohardened by blanket irradiation and/or thermal curing to help form an encapsulating structure. In addition, the composition also incorporates one or more other, non-diffusing binder components that may be thermosetting or thermoplastic. The end result is an encapsulated structure with good hardness, durability, dimensional stability, resilience, and toughness.

STATEMENT OF PRIORITY

This application claims the priority of U.S. Provisional Application No.60/211,709 filed Jun. 15, 2000, the entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

This invention relates to the use of multiphoton-inducedphotopolymerization methods for fabricating optically functionalelements (e.g., waveguides, diffraction gratings, splitters, couplers,lenses, ring resonators, other optical circuitry, and the like, etc.)that find particular utility in optical communication systems.

BACKGROUND OF THE INVENTION

Optical interconnects and integrated circuits may be used, in oneapplication, to optically connect one or more optical fibers to one ormore remote sites, typically other optical fibers. For example, wherelight is carried by one or more input fiber(s), the light may betransferred to, split between, or merged into one or more remote sites.Active or passive devices within the optical integrated circuit may alsomodulate or switch the input signal. Optical interconnects play animportant role in fiber telecommunication, cable television links, anddata communication. A waveguide is a type of optical interconnect.

For the most part, commercially available optical interconnects havebeen made of glass. Such interconnects, or couplers, are generally madeby fusing glass optical fibers or by attaching glass fibers to a planar,glass integrated optical device that guides light from input fiber(s) tooutput fiber(s) attached to different ends of the device. Bothapproaches are labor intensive and costly. The cost increasesproportionately with the number of fibers used due to the additionallabor needed to fuse or attach each individual fiber. Such intensivelabor inhibits mass production of these devices.

A further problem results from the mismatch in shape of the opticalmodes in the glass fiber and the integrated optical device. Glass fibercores are typically round, whereas the channel guides tend to haverectilinear cross-sections. This mismatch tends to cause insertionlosses when a fiber is butt coupled to an integrated optical device.Thus, there is a strong need for an integrated optical device orinterconnect that can be easily attached to optical fibers with goodmode matching.

As compared to glass structures, polymeric optical structures offer manypotential advantages, and it would be desirable to have polymericoptical elements that could satisfy the demands of thetelecommunications and data communications industries. Advantages ofpolymeric elements would include versatility of fabrication techniques(such as casting, solvent coating, and extrusion followed by directphoto-patterning), low fabrication temperatures (down to roomtemperature, allowing compatibility with a greater variety of othersystem components and substrates than is possible with the highprocessing temperatures characteristic of inorganic materials), and thepotential ability to fabricate unique devices in three dimensions, allof which could lead to lower cost and high volume production.

Unlike glass optical interconnects, two-dimensional, polymeric channelwaveguides are relatively easily produced. Numerous methods forfabricating polymeric waveguides have been developed. For example,electroplating nickel onto a master to form a channel waveguide mold andusing photoresist techniques to form waveguide channels have been knownfor years. Cast-and-cure methods have supplemented older injectionmolding methods of forming polymeric channel waveguides. Followingformation of the channel waveguide, further cladding and protectivecoatings typically is added inasmuch as polymeric waveguides generallymust be protected from the environment to prevent moisture uptake ordamage that could adversely affect performance.

The manufacture of other three dimensional, micro-optical elements hasbeen quite challenging. Ion diffusion methods involve complex, multistepprocesses to build three dimensional structures. Photolithographictechniques, e.g., photoresist reflow, have been used to make lenses andthe like. However, the range of shapes that can be made usinglithography are limited by a number of factors including surface tensioneffects. Photolithography also is limited to the fabrication of elementswhose optical axis is normal to the substrate upon which the element isfabricated. It is difficult, for instance, to make elements withaccurate undercuts using photolithography.

U.S. Pat. No. 5,402,514 describes a different approach for manufacturinga polymeric, three dimensional interconnect by laminating dry filmstogether. In these laminate structures, the outer layer(s) function asthe cladding and the inner layers incorporate the optical circuitry.Single photon photopolymerization is used to photocure portions of eachlamina. In order to build up three-dimensional circuitry using thisapproach, multiple exposure steps would be required to form eachphotocured lamina. Alignment of the layers during assembly to form thelaminate structure could also prove problematic. The layers would alsobe subject to delamination if the bond quality between layers is poor.

Multiphoton polymerization techniques offer the potential to fabricatethree dimensional optical structures more conveniently. Moleculartwo-photon absorption was predicted by Goppert-Mayer in 1931. Upon theinvention of pulsed ruby lasers in 1960, experimental observation oftwo-photon absorption became a reality. Subsequently, two-photonexcitation has found application in biology and optical data storage, aswell as in other fields.

There are two key differences between two-photon induced photoprocessesand single-photon induced processes. Whereas single-photon absorptionscales linearly with the intensity of the incident radiation, two-photonabsorption scales quadratically. Higher-order absorptions scale with arelated higher power of incident intensity. As a result, it is possibleto perform multiphoton processes with three-dimensional spatialresolution. Also, because multiphoton processes involve the simultaneousabsorption of two or more photons, the adsorbing chromophore is excitedwith a number of photons whose total energy equals the energy of anexcited state of the chromophore, even though each photon individuallyhas insufficient energy to excite the chromophore. Because the excitinglight is not attenuated by single-photon absorption within a curablematrix or material, it is possible to selectively excite molecules at agreater depth within a material than would be possible via single-photonexcitation by use of a beam that is focused to that depth in thematerial. These two phenomena also apply, for example, to excitationwithin tissue or other biological materials.

Major benefits have been foreshadowed by applying multiphoton absorptionto the areas of photocuring and microfabrication. For example, inmultiphoton lithography or stereolithography, the nonlinear scaling ofmultiphoton absorption with intensity has provided the ability to writefeatures having a size that is less than the diffraction limit of thelight utilized, as well as the ability to write features in threedimensions (which is also of interest for holography).

The use of multiphoton-induced photopolymerization has been described inMukesh P. Joshi et al., “Three-dimensional optical circuitry usingtwo-photo-assisted polymerization,” Applied Physics Letters, Volume 74,Number 2, Jan. 11, 1999, pp. 170–172; Cornelius Diamond et al.,“Two-photon holography in 3-D photopolymer host-guest matrix,” OPTICSEXPRESS, Vol. 6, No. 3, Jan. 31, 2000, pp. 64–68; Cornelius Diamond,“OMOS: Optically Written Micro-Optical Systems in Photopolymer,” Ph.D.Thesis, January 2000; Brian H. Cumpston et al., “Two-photonpolymerization initiators for three-dimensional optical data storage andmicrofabrication,” NATURE, Vol. 398, Mar. 4, 1999, pp. 51–54; T. J.Bunning et al., “Electrically Switchable Gratings Formed Using UltrafastHolographic Two-Photon-Induced Photopolymerization,” Chem. Mater. 2000,12, 2842–2844; Cornelius Diamond et al., “Two-photon holography in 3-Dphotopolymer host-guest matrix: errata,” OPTICS EXPRESS, Vol. 6, No. 4,Feb. 14, 2000, pp. 109–110; S. M. Kirkpatrick et al., “Holographicrecording using two-photon-induced photopolymerization,” Appl. Phys. A69, 461–464 (1999); Hong-Bo Sun et al., “Three-dimensional photoniccrystal structures achieved with two-photon-absorptionphotopolymerization of resin,” APPLIED PHYSICS LETTERS, Volume 74,Number 6, Feb. 8, 1999, pp. 786–788; Kevin D. Belfield et al., “Near-IRTwo-Photon Photoinitiated Polymerization Using a Fluorone/AmineInitiating System,” J. Am. Chem. Soc. 2000, 122, 1217–1218.

The stability and quality of three dimensional optical structures madeusing multiphoton polymerization techniques remains a concern. Elementsmade to date have not been made in fully cured materials, thus, havingpoor stability, especially when exposed to light. Others are freestanding and are not encapsulated, thus being sensitive to thesurrounding environment and having potential stability issues relativeto optical performance. It is also more challenging to achieve highcircuit density when the boundaries between adjacent elements cannot becontrolled with sufficient precision. Other methods have providedelements whose shape, index of refraction properties, and/or other orchemical physical properties degrade in a relatively short time.

Thus, there remains a strong need in the art for direct fabrication ofthree dimensional, stable polymeric optical elements with a high degreeof precision, as desired. There is also a need for an approach thatallows devices to be coupled together with low insertion losses and goodmode matching.

SUMMARY OF THE INVENTION

The present invention provides methods of fabricating three dimensional,stable optical elements with a high degree of precision. Imagewisemultiphoton polymerization and blanket irradiation techniques arecombined to fabricate such optical elements in situ in an encapsulating,protective monolithic polymeric matrix. Imagewise, multi-photonpolymerization techniques are used to form the optical element within abody incorporating multiphoton polymerizable material. The bodysurrounding the optical element is also photohardened by blanketirradiation and/or thermal curing to help form an encapsulatingstructure. The end result is an encapsulated structure with goodresolution, hardness, durability, dimensional stability, resilience,refractive index contrast, and toughness.

Thus, in one aspect, the present invention relates to a method offabricating an encapsulated optical element. A body is provided thatincludes:

(i) a photopolymerizable precursor comprising a diffusing species, saidprecursor forming a polymer matrix upon photopolymerization, and saidmatrix having an index of refraction;

(ii) a substantially non-diffusing binder component having an index ofrefraction that is lower than the index of refraction of the polymermatrix and that is miscible with the photopolymerizable precursor; and

(iii) a multiphoton photoinitiator system. At least a portion of thebody is imagewise exposed to a multiphoton polymerizing fluence ofenergy under conditions effective to photopolymerize the polymerprecursor in a pattern effective to form a three-dimensional opticalelement. After imagewise exposing the body, at least a portion of thebody is non-imagewise exposed, e.g., via blanket irradiation, to aphotopolymerizing fluence of energy under conditions such that amonolithic encapsulating matrix is formed around at least a portion ofthe optical element.

The present invention also provides an innovative method for couplingtwo optical elements together wherein the juncture between the twoelements is formed in situ. The method reduces insertion losses andprovides good mode matching. In one such aspect, the present inventionrelates to a method of coupling a first optical device to a secondoptical device, comprising the steps of:

(a) providing the first optical device, said first optical deviceincluding a partially formed, first optical element at least partiallyencapsulated in ingredients comprising photocurable functionality; andwherein said partially formed, first optical element has an end that isspaced apart from a boundary of the first optical device by a regioncomprising a photocurable material;

(b) positioning the first optical device adjacent to the second opticaldevice such that the end of the first optical element is at leastapproximately juxtaposed in alignment with an end of a second opticalelement incorporated into the second optical device, wherein the regionincluding photocurable material is positioned between said ends; and

(c) photocuring by multiphoton induced polymerization at least a portionof said region under conditions such that the ends of the first andsecond optical elements are optically coupled together.

In a preferred aspect of coupling two optical devices together in situ,the present invention relates to a method of coupling a first opticaldevice to a second optical device, comprising the steps of:

(a) providing the first optical element device, said first deviceincluding a partially formed, first optical element at least partiallyencapsulated in ingredients comprising a binder, a photocurable matrixprecursor, and a multiphoton photoinitiator system, said partiallyformed optical element having an end that is spaced apart from aboundary of the body such that a multiphoton photocurable region isjuxtaposed between the end and the boundary;

(b) providing the second optical element device, said second deviceincluding a second optical element having an end to be coupled to thefirst optical element;

(c) positioning the first optical element device adjacent the secondoptical element device to at least approximately juxtapose the ends ofthe first and second optical elements in alignment with each other,wherein the multiphoton photocurable region is positioned between saidends; and

(d) photocuring at least a portion of said region under conditions suchthat the ends of the first and second optical elements are opticallycoupled together.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other advantages of the present invention, andthe manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of the embodiments of the invention taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a schematic representation of a system for fabricating anencapsulated optical element of the present invention, showing howmultiphoton absorption causes photopolymerization within the focalregion of laser light directed into a photopolymerizable body;

FIG. 2 is a schematic representation of the system of FIG. 1, showinghow imagewise exposure formed an optical element in the body;

FIG. 3 schematically shows the body of FIG. 2 being blanket irradiated;

FIG. 4 schematically shows the body of FIG. 3 being heated to cure athermosetting polymer included in the body; and

FIG. 5 schematically illustrate a preferred mode of implementing thepresent invention in which a partially completed encapsulated opticalelement is completed in situ to couple the element to another opticaldevice.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

Preferred embodiments of the present invention provide methods ofpreparing optical elements within an encapsulating binder matrix. Thepreferred methods involve multiphoton-initiated photopolymerization ofselected portions of a body by which optical element(s), e.g., thosewith simple or complex two or three-dimensional geometries, can beformed within the body. In addition to the photopolymerizable material,the composition also includes a substantially non-diffusing bindercomponent that provides, among other advantages, a stable backgroundwithin which to form the optical element with good resolution. Afterformation of the optical element, the resultant optical element may bestably encased within some or all of the remaining material by blanketirradiation of the body or other curing, as desired. Blanket irradiationof the body may occur with energy that causes photopolymerization bymechanism(s) involving single and/or multiphoton absorption. Thus, anyremaining photopolymerizable material is rendered insensitive to furtherexposure, enhancing the stability of the structure.

Notwithstanding the blanket irradiation of the body, the separatelyphotopolymerized optical element nonetheless retains refractive indexcontrast with the surrounding photopolymerized matrix. Depending uponwhether the non-diffusing binder component is thermosetting, it, too,may be cured via blanket irradiation (if it has photopolymerizablefunctionality), thermal energy, chemical crosslinking, or the like. Theresultant encapsulated optical elements are useful in integrated optics,for example.

FIGS. 1 through 4 schematically illustrate one preferred methodology ofthe present invention in more detail. Referring to FIG. 1, system 10includes laser light source 12 that directs laser light 14 throughoptical lens 16. Lens 16 focuses laser light 14 at focal region 18within body 20 that includes photopolymerizable constituent(s). Laserlight 14 has an intensity, and the multiphoton photosensitizer has anabsorption cross-section such that the light intensity outside of thefocal region is insufficient to cause multiphoton absorption, whereasthe light intensity in the portion of the photopolymerizable compositioninside the focal region 18 is sufficient to cause multiphoton absorptioncausing photopolymerization within such focal region 18. In practicaleffect, this means that the volume of photopolymerizable compositionwithin the focal region 18 will harden via photocuring, while portionsof the composition outside of the focal region 18 are substantiallyunaffected.

A suitable translation mechanism 24 provides relative movement betweenbody 20, Lens 16, and/or and focal region 18 in three dimensions toallow focal region 18 to be positioned at any desired location withinbody 20. This relative movement can occur by physical movement of lightsource 12, lens 16, and/or body 20. Through appropriate exposure ofsuccessive regions of body 20, and/or through holographic exposure, inan imagewise fashion, the corresponding photopolymerized portions ofbody 12 may form one or more three-dimensional structures within body 20that are refractive index images of three dimensional structures. Onesuitable system would include a mirror-mounted galvonometer with amoving stage.

Useful exposure systems include at least one light source (usually apulsed laser) and at least one optical element. Preferred light sourcesinclude, for example, femtosecond near-infrared titanium sapphireoscillators (for example, a Coherent Mira Optima 900-F) pumped by anargon ion laser (for example, a Coherent Innova). This laser, operatingat 76 MHz, has a pulse width of less than 200 femtoseconds, is tunablebetween 700 and 980 nm, and has average power up to 1.4 Watts.

Another example is a Spectra Physics “Mai Tai” Ti:sapphire laser system,operating at 80 MHz, average power about 0.85 Watts, tunable from 750 to850 nm, with a pulse width of about 100 femtoseconds. However, inpractice, any light source that provides sufficient intensity (to effectmultiphoton absorption) at a wavelength appropriate for thephotosensitizer (used in the photoreactive composition) can be utilized.Such wavelengths can generally be in the range of about 300 to about1500 nm; preferably, from about 600 to about 1100 nm; more preferably,from about 750 to about 850 nm.

Q-switched Nd:YAG lasers (for example, a Spectra-Physics Quanta-RayPRO), visible wavelength dye lasers (for example, a Spectra-PhysicsSirah pumped by a Spectra-Physics Quanta-Ray PRO), and Q-switched diodepumped lasers (for example, a Spectra-Physics FCbar™) also can beutilized.

One skilled in the art can choose appropriate settings to use such lasersystems to carry out multiphoton polymerization. For example, pulseenergy per square unit of area (Ep) can vary within a wide range andfactors such as pulse duration, intensity, and focus can be adjusted toachieve the desired curing result in accordance with conventionalpractices. If Ep is too high, the material being cured can be ablated orotherwise degraded. If Ep is too low, curing may not occur or may occurtoo slowly.

In terms of pulse duration when using near infrared pulsed lasers, apreferred pulse length is generally less than about 10⁻⁸ second, morepreferably less than about 10⁻⁹ second, and most preferably less thanabout 10⁻¹¹ second). Laser pulses in the femtosecond regime are mostpreferred as these provide a relatively large window for setting Eplevels that are suitable for carrying out multiphoton curing. Withpicosecond pulses, the operational window is not as large. Withnanosecond pulses, curing may proceed slower than might be desired insome instances or not at all, because the Ep level may need to beestablished at a low level to avoid material damage when the pulses areso long, relatively.

Advantageously, the fabrication method of the present invention allowsthe use, if desired, of laser light 14 having a wavelength within oroverlapping the range of wavelengths of light to be carried by waveguide26. This could be desirable because the photoinitiator used absorbs athalf the wavelength of the laser line, and so does not attenuate thefundamental. This results in greater latitude in selecting materials forfabricating the optical element or waveguide to minimize absorption ofdesired wavelengths of light to be carried by the optical element orwaveguide. In some embodiments, therefore, laser light 14 may have awavelength that is substantially the same as the wavelength of light tobe carried by waveguide 26. In this context, “substantially the same”means within 10%, preferably within 5%, and more preferably within 1%.

Although lens 16 is shown, other optical elements useful in carrying outthe method of the invention can be used to focus light 14 and include,for example, one or more of refractive optical elements (for example,lenses), reflective optical elements (for example, retroreflectors orfocusing mirrors), diffractive optical elements (for example, gratings,phase masks, and holograms), diffusers, splitters, couplers, lenses,pockels cells, ring resonators, wave guides, and the like. Such opticalelements are useful for focusing, beam delivery, beam/mode shaping,pulse shaping, and pulse timing. Generally, combinations of opticalelements can be utilized, and other appropriate combinations will berecognized by those skilled in the art. It is often desirable to useoptics with large numerical aperture characteristics to providehighly-focused light. However, any combination of optical elements thatprovides a desired intensity profile (and spatial placement thereof) canbe utilized. For example, the exposure system can include a scanningconfocal microscope (BioRad MRC600) equipped with a 0.75 NA objective(Zeiss 20X Fluar).

Exposure times and scan rates generally depend upon the type of exposuresystem used to cause image formation and its accompanying variables suchas numerical aperture, geometry of light intensity spatial distribution,the peak light intensity during the laser pulse (higher intensity andshorter pulse duration roughly correspond to peak light intensity), aswell as upon the nature of the composition exposed (and itsconcentrations of photosensitizer, photoinitiator, and electron donorcompound). Generally, higher peak light intensity in the regions offocus allows shorter exposure times, everything else being equal. Linearimaging or “writing” speeds generally can be about 5 to 100,000microns/second using a laser pulse duration of about 10E-8 to 10E-15seconds preferably, about 10E-12 to 10E-14 seconds) and about 10E3 to10E9 pulses per second (preferably, about 10E5 to 10E8 pulses persecond).

FIG. 2 shows how imagewise exposure of selected portions of body 20 formphotopolymerized, three-dimensional waveguide 26 within body 20.Portions 28 of body 20 that are outside the photopolymerized portionsconstituting waveguide 26 remain unphotopolymerized at this stage ofthis embodiment. As a consequence of imagewise photopolymerization, therefractive index of waveguide 26 will be increased relative to that ofuncured portions 28. This contrast is generally sufficient to providewaveguiding or other desired optical functionality.

In theory, the waveguide formation is believed to be due, at least inpart, to an increase in density of the cured material relative to theuncured material. Upon exposure to the laser light, amultiphoton-induced, photopolymerization reaction occurs in the focalregion 18. It is believed that there is then some interdiffusion ofrelatively low molecular weight species into the exposed region from theunexposed regions, at least near the interface of these regions. Thisinterdiffusion alters and typically further increases the density of theexposed region, raising its refractive index. At the same time, theconcentration of the diffusing species is depleted from the unexposedregion proximal to the interface, further enhancing the refractive indexcontrast between the regions. In short, it is believed that thisdiffusion forms a so-called depletion zone (in the sense that theconcentration of diffusing species in the zone is reduced) at thedesired optical element boundary, contributing important opticalcontrast between the element boundary and the surrounding encapsulatingmaterial.

A significant advantage of the present invention is that the refractiveindex profile of the element may be controlled through shaping the modeprofile of the writing beam. This is useful for mode matching to otherelements and optimizing the mode profile in the optical element 26. Therefractive index profile may be further controlled through appropriatechoice of one or more other factors, such as the Tg of the binder,monomer size (in order to control the diffusion rate), and temperatureof the sample during exposure. For instance, because the distance amonomer molecule can diffuse depends to some degree on its probabilityof reaction with a growing polymer chain, diffusion can be controlled bycontrolling such factors as the waveguide width; the time, intensity,and intensity distribution of the exposure; the concentration of thephotoinitiator system, and the reactivity and functionality of themonomer or monomers. Since diffusion is a function of molecular weight,shape, and size, monomer diffusion can be controlled by controlling themolecular weight, shape, and size of the monomer or monomers. Diffusioncan also be controlled by controlling the viscosity of the monomer ormonomers, as well as the glass transition point of the binder. Sincesome of these properties, such as viscosity also vary with temperature,variation of temperature and some other factor at the same time mayproduce a complex interaction. Other variables are the time betweenexposure and the blanket irradiation step (described below) and thetemperature at which the element is stored during the period betweenmultiphoton curing and blanket irradiation.

FIG. 3 illustrates the step in which body 20 is blanket irradiated,i.e., nonimagewise irradiated, from source 30 with a fluence of energy32 of a type for which at least the uncured portions 28, and morepreferably at least the substantial entirety of body 20 has an opticalcross-section for absorption of such energy sufficient to causephotopolymerization of the blanket irradiated portions of body 20.Blanket irradiation can occur using appropriate energy, of an intensityand type effective to induce single and/or multiphotonphotopolymerization. As a consequence of blanket irradiation, thephotopolymerizable material in uncured portions 28 are cured andhardened, thus encapsulating at least portions of waveguide 26 in amonolithic polymer matrix. The resultant encapsulating structure helpsto protect and stabilize waveguide 26. Significantly, even thoughblanket irradiation might cause photopolymerization through the entiretyof body 20, sufficient index of refraction contrast between waveguide 26and cured portions 28 to support waveguiding is maintained. Preferably,such contrast is greater than 0.03, more preferably greater than 0.04,most preferably greater than 0.05. As described below, it is believedthat the formation of a so-called depletion zone at the boundary of thecured optical element via diffusion of low molecular weight specieshelps to provide such optical contrast.

Advantageously, blanket irradiation promotes dimensional and chemicalstability of the structure. Continued diffusion over time might changethe shape and refractive index profile of the optical element.Additionally, after blanket irradiation, most, if not all, of thepolymerizable species in the composition have been polymerized,rendering the composition chemically inert with respect to furtherirradiation, heating, or chemical reaction involving polymerization orcrosslinking, providing stable, reliable optical elements/devices withimproved physical properties compared to the same without blanketirradiation. Additionally, there is reduced potential for health hazardsdue to the absence, or near absence, of unpolymerized polymer precursorin the finished device after blanket irradiation.

The energy source used for achieving blanket irradiation may be actinic(e.g., radiation having a wavelength in the ultraviolet or visibleregion of the spectrum), accelerated particles (e.g., electron beamradiation), thermal (e.g., heat or infrared radiation), or the like.Preferably, the energy is actinic radiation or accelerated particles,because such energy provides excellent control over the initiation andrate of curing. Additionally, actinic radiation and acceleratedparticles can be used for curing at relatively low temperatures. Thisavoids degrading components that might be sensitive to the relativelyhigh temperatures that might be required to initiate curing of thephotopolymerizable groups when using thermal curing techniques. Suitablesources of actinic radiation include mercury lamps, xenon lamps, carbonarc lamps, tungsten filament lamps, lasers, electron beam energy,sunlight, and the like.

FIG. 4 shows an optional step in which the optically functional,composite structure resulting from the blanket irradiation step and/orimagewise exposure step is heated by heat source 34 to further cureother any thermosetting materials included in the structure. This stepis particularly advantageous when the substantially non-diffusing bindercomponent includes nonphotopolymerizable, yet curable thermosettingpolymers that undergo crosslinking when heated. Thermally induced curingmay optionally occur with or without a suitable catalyst depending uponthe nature of the thermosetting material.

In some embodiments, it can be appreciated that any such thermosettingpolymer(s) and the cured photopolymers could form, if desired,entangled, yet substantially separate polymer matrices in which thereare substantially no covalent bonds between the two matrices. Suchentangled polymer matrices are generally referred to in the art asinterpenetrating polymer networks, or IPN's. As another possibility, thematerials that form body 20 may include a thermoplastic polymer thatdoes not undergo crosslinking reactions nor covalent bonding with thephotopolymerized polymer matrix, yet these may still comprise polymerchains that are entangled within the photopolymerized polymer matrix.Such entangled matrices are generally referred to in the art assemi-interpenetrating polymer networks, or semi-IPN's. The nature of thethermoplastic and/or thermoplastic polymer constituents, if any, as wellas other compositional aspects of the photopolymerizable compositionincorporated into body 20 will be described in more detail below.

Generally, the materials that constitute body 20 of FIG. 1 generallyinclude (1) a photopolymerizable precursor that forms a cured polymermatrix upon photopolymerization and that incorporates a diffusingspecies; (2) a substantially non-diffusing binder component that has anindex of refraction that is optically contrastable to and lower than theindex of refraction of the photocured polymer matrix and that ismiscible with the photopolymerizable precursor; and (3) a multiphotonphotoinitiator system that preferably includes a multiphotonphotosensitizer and optionally at least one photoinitiator that iscapable of being photosensitized by the photosensitizer. Optionally, themultiphoton photoinitiator system may also include an electron donor.

As used herein, “photopolymerizable” refers to functionality directly orindirectly pendant from a monomer, oligomer, and/or polymer backbone (asthe case may be) that participates in curing reactions upon exposure toa suitable source of curing energy. Such functionality generallyincludes not only groups that cure via a cationic mechanism uponradiation exposure but also groups that cure via a free radicalmechanism. Representative examples of such photopolymerizable groupssuitable in the practice of the present invention include epoxy groups,(meth)acrylate groups, olefinic carbon-carbon double bonds, allyloxygroups, alpha-methyl styrene groups, (meth)acrylamide groups, cyanateester groups, vinyl ethers groups, combinations of these, and the like.Free radically polymerizable groups are preferred. Of these, (meth)acrylmoieties are most preferred. The term “(meth)acryl”, as used herein,encompasses acryl and/or methacryl.

As used herein, the term “monomer” means a relatively low molecularweight material (i.e., having a molecular weight less than about 500g/mole) having one or more polymerizable groups. “Oligomer” means arelatively intermediate molecular weight (i.e., having a molecularweight of from about 500 up to about 10,000 g/mole) material having oneor more polymerizable groups. “Polymer” means a relatively largemolecular weight (i.e., about 10,000 g/mole or more) material that mayor may not have available curing functionality. The term “molecularweight” as used throughout this specification means average molecularweight unless expressly noted otherwise. As used herein, the term“resin” shall be used to refer collectively to oligomers and polymers.

The photopolymerizable precursor preferably includes one or moremonomers, oligomers, and/or polymers with photopolymerizablefunctionality. Preferably, the precursor includes at least one suchmonomer. Subject to desired performance standards, anyphotopolymerizable monomer or combinations thereof may be incorporatedinto the photopolymerizable precursor. Accordingly, the presentinvention is not intended to be limited to specific kinds ofphotopolymerizable monomers in various aspects so long as any suchperformance conditions are satisfied. In addition to photopolymerizablefunctionality, the monomers incorporated into the photopolymerizableprecursor may include other functionality or multiple functionality ofthe same and/or different type.

The photopolymerizable monomers may be mono-, di-, tri-, tetra- orotherwise multifunctional in terms of photopolymerizable moieties. Theamount of such monomers to be incorporated into the photopolymerizableprecursor can vary within a wide range depending upon the intended useof the resultant composition. As general guidelines, thephotopolymerizable precursor may contain from about 10 to about 100,preferably 20 to 90 weight percent of such monomers. Monomers are lowmolecular weight materials that function as diffusing species in theprecursor composition.

Representative examples of monofunctional, photopolymerizable monomerssuitable for use in the photopolymerizable precursor include(meth)acrylamide, (meth)acrylic acid, (meth)acrylonitrile,1,2,4-butanetriol tri(meth)acrylate, 1,3-propanediol di(meth)acrylate,1,4-cyclohexanediol di(meth)acrylate, 2-(2-ethoxyethoxy)ethyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, acrylated oligomers such as those of U.S. Pat. No.4,642,126); allyl acrylate, alpha-epoxide, alpha-methylstyrene,beta-carboxyethyl (meth)acrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,copolymerizable mixtures of (meth)acrylated monomers, diallyl phthalate,diethyleneglycol diacrylate, divinyl adipate, divinyl phthalate; divinylsuccinate, dodecyl (meth)acrylate, ethyl (meth)acrylate, ethyleneglycoldi(meth)acrylate, glycerol di(meth)acrylate, glycerol tri(meth)acrylate,hexyl (meth)acrylate, hydroxy functional caprolactone ester(meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyethyl(meth)acrylate, hydroxyisobutyl (meth)acrylate, etrahydrofurfuryl(meth)acrylate, hydroxymethyl (meth)acrylate, hydroxypropyl(meth)acrylate, hydroxyisopropyl (meth)acrylate, isobornyl(meth)acrylate, isobutyl (meth)acrylate, isodecyl (meth)acrylate,isononyl (meth)acrylate, isooctyl (meth)acrylate, isopropylmethacrylate, itaconic acid, lauryl (meth)acrylate, maleic anhydride,methyl (meth)acrylate, methyl (meth)acrylate, n-butyl (meth)acrylate,n-hexyl (meth)acrylate, nonylphenol ethoxylate (meth)acrylate,N-substituted (meth)acrylamide, N-vinyl-2-pyrrolidone,N-vinylcaprolactam, octyl (meth)acrylate, sorbitol hex(meth)acrylate,stearyl (meth)acrylate, stearyl (meth)acrylate, styrene, substitutedstyrene, the bis-acrylates and bis-methacrylates of polyethylene glycolsof molecular weight about 200–500, unsaturated amides (for example,methylene bis-(meth)acrylamide, methylene bis-(meth)acrylamide,1,6-hexamethylene bis-(meth)acrylamide, diethylene triaminetris-(meth)acrylamide and beta-(meth)acrylaminoethyl (meth)acrylate);vinyl esters, vinyl ethers, combinations of these and the like. Suitableethylenically-unsaturated species also are described, for example, byPalazzotto et al. in U.S. Pat. No. 5,545,676 at column 1, line 65,through column 2, line 26 as well as in U.S. Pat. No. 4,652,274, andU.S. Pat. No. 4, 642,126).

Preferred monofunctional (meth)acrylates including those withsubstituted and unsubstituted aromatic groups, such as phenoxyethyl(meth)acrylate, 2-(1-naphthoxy)ethyl(meth)acrylate, 2-(2-naphthoxy)ethylacrylate, alkoxylated nonylphenol acrylate, and9-phenanthrylmethyl(meth)acrylate.

Multifunctional photopolymerizable monomers comprising, on average,greater than one photopolymerizable group per molecule, may also beincorporated into the photopolymerizable precursor to enhance one ormore properties of the cured structures, including crosslink density,hardness, tackiness, mar resistance, or the like. If one or moremultifunctional materials are present, the photopolymerizable precursormay comprise from 0.5 to about 50, preferably 0.5 to 35, and morepreferably from about 0.5 to about 25 weight percent of such materials.Examples of such higher functional, photopolymerizable monomers includeethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate,triethylene glycol di(meth)acrylate, tetraethylene glycoldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylatedtrimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate,pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,and neopentyl glycol di(meth)acrylate, combinations of these, and thelike. Preferred multifinctional (meth)acrylates include those withsubstituted and unsubstituted aromatic groups, such as ethoxylatedbisphenol A di(meth)acrylate, aromatic urethane (meth)acrylates (Such asM-Cure™203 and CN972 and CN1963, Sartomer, Inc.), and aromatic epoxy(meth)acrylates (such as CN-120, CN-124, and CN-151, Sartomer, Inc.)

While not preferred, the photopolymerizable precursor may also includeone or more resins having photopolymerizable functionality. If present,the photopolymerizable precursor may include 1 to 50 parts by weight ofsuch one or more photopolymerizable resins per 100 parts by weight ofthe precursor. Suitable reactive polymers include polymers with pendant(meth)acrylate groups, for example, having from 1 to about 50(meth)acrylate groups per polymer chain. Examples of such polymersinclude aromatic acid (meth)acrylate half ester resins such as Sarbox™resins available from Sartomer (for example, Sarbox™ 400, 401, 402, 404,and 405). Other useful reactive polymers curable by free radicalchemistry include those polymers that have a hydrocarbyl backbone andpendant peptide groups with free-radically polymerizable functionalityattached thereto, such as those described in U.S. Pat. No. 5,235,015(Ali et al.). Mixtures of two or more monomers, oligomers, and/orreactive polymers can be used if desired. Preferredethylenically-unsaturated species include acrylates, aromatic acid(meth)acrylate half ester resins, and polymers that have a hydrocarbylbackbone and pendant peptide groups with free-radically polymerizablefunctionality attached thereto.

Suitable cationically-reactive species are described, for example, byOxman et al. in U.S. Pat. Nos. 5,998,495 and 6,025,406 and include epoxyresins. Such materials, broadly called epoxides, include monomeric epoxycompounds and epoxides of the polymeric type and can be aliphatic,alicyclic, aromatic, or heterocyclic. These materials generally have, onthe average, at least 1 polymerizable epoxy group per molecule(preferably, at least about 1.5 and, more preferably, at least about 2).The polymeric epoxides include linear polymers having terminal epoxygroups (for example, a diglycidyl ether of a polyoxyalkylene glycol),polymers having skeletal oxirane units (for example, polybutadienepolyepoxide), and polymers having pendant epoxy groups (for example, aglycidyl methacrylate polymer or copolymer). The epoxides can be purecompounds or can be mixtures of compounds containing one, two, or moreepoxy groups per molecule. These epoxy-containing materials can varygreatly in the nature of their backbone and substituent groups. Forexample, the backbone can be of any type and substituent groups thereoncan be any group that does not substantially interfere with cationiccure at room temperature. Illustrative of permissible substituent groupsinclude halogens, ester groups, ethers, sulfonate groups, siloxanegroups, nitro groups, phosphate groups, and the like. The molecularweight of the epoxy-containing materials can vary from about 58 to about100,000 or more.

Useful epoxy-containing materials include those which containcyclohexene oxide groups such as epoxycyclohexanecarboxylates, typifiedby 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. A moredetailed list of useful epoxides of this nature is set forth in U.S.Pat. No. 3,117,099.

Other epoxy-containing materials that are useful include glycidyl ethermonomers of the formula

where R′ is alkyl or aryl and n is an integer of 1 to 6. Examples areglycidyl ethers of polyhydric phenols obtained by reacting a polyhydricphenol with an excess of a chlorohydrin such as epichlorohydrin (forexample, the diglycidyl ether of2,2-bis-(2,3-epoxypropoxyphenol)-propane). Additional examples ofepoxides of this type are described in U.S. Pat. No. 3,018,262, and inHandbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Co., NewYork (1967).

Numerous commercially available epoxy resins can also be utilized. Inparticular, epoxides that are readily available include octadecyleneoxide, epichlorohydrin, styrene oxide, vinyl cyclohexene oxide,glycidol, glycidylmethacrylate, diglycidyl ethers of Bisphenol A (forexample, those available under the trade designations Epon™ 828, Epon™825, Epon™ 1004, and Epon™ 1010 from Resolution Performance Products,formerly Shell Chemical Co., as well as DER™-331, DER™-332, and DER™-₃₃₄from Dow Chemical Co.), vinylcyclohexene dioxide (for example, ERL-4206from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (for example,ERL-4221 or Cyracurem™ UVR 6110 or UVR 6105 from Union Carbide Corp.),3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclohexenecarboxylate (for example, ERL-4201 from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate (for example, ERL-4289from Union Carbide Corp.), bis(2,3-epoxycyclopentyl) ether (for example,ERL-0400 from Union Carbide Corp.), aliphatic epoxy modified frompolypropylene glycol (for example, ERL-4050 and ERL-4052 from UnionCarbide Corp.), dipentene dioxide (for example, ERL-4269 from UnionCarbide Corp.), epoxidized polybutadiene (for example, Oxiron™ 2001 fromFMC Corp.), silicone resin containing epoxy functionality, flameretardant epoxy resins (for example, DER™-580, a brominated bisphenoltype epoxy resin available from Dow Chemical Co.), 1,4-butanedioldiglycidyl ether of phenolformaldehyde novolak (for example, DEN™-431and DEN™-438 from Dow Chemical Co.), resorcinol diglycidyl ether (forexample, Kopoxite™ from Koppers Company, Inc.),bis(3,4-epoxycyclohexyl)adipate (for example, ERL-4299 or UVR-6128, fromUnion Carbide Corp.), 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane (for example, ERL-4234 from Union CarbideCorp.), vinylcyclohexene monoxide 1,2-epoxyhexadecane (for example,UVR-6216 from Union Carbide Corp.), alkyl glycidyl ethers such as alkylC₈–C₁₀ glycidyl ether (for example, Heloxy™ Modifier 7 from ResolutionPerformance Products), alkyl C₁₂–C₁₄ glycidyl ether (for example,Heloxy™ Modifier 8 from Resolution Performance Products), butyl glycidylether (for example, Heloxy™ Modifier 61 from Resolution PerformanceProducts), cresyl glycidyl ether (for example, Heloxy™ Modifier 62 fromResolution Performance Products), p-tert-butylphenyl glycidyl ether (forexample, Heloxy™ Modifier 65 from Resolution Performance Products),polyfunctional glycidyl ethers such as diglycidyl ether of1,4-butanediol (for example, Heloxy™ Modifier 67 from ResolutionPerformance Products), diglycidyl ether of neopentyl glycol (forexample, Heloxy™ Modifier 68 from Resolution Performance Products),diglycidyl ether of cyclohexanedimethanol (for example, Heloxy™ Modifier107 from Resolution Performance Products), trimethylol ethanetriglycidyl ether (for example, Heloxy™ Modifier 44 from ResolutionPerformance Products), trimethylol propane triglycidyl ether (forexample, Heloxy™ Modifier 48 from Resolution Performance Products),polyglycidyl ether of an aliphatic polyol (for example, Heloxy™ Modifier84 from Resolution Performance Products), polyglycol diepoxide (forexample, Heloxy™ Modifier 32 from Resolution Performance Products),bisphenol F epoxides (for example, Epon™-1138 or GY-281 from Ciba-GeigyCorp.), and 9,9-bis[4-(2,3-epoxypropoxy)-phenyl]fluorenone (for example,Epon™ 1079 from Resolution Performance Products).

Other useful epoxy resins comprise copolymers of acrylic acid esters ofglycidol (such as glycidylacrylate and glycidylmethacrylate) with one ormore copolymerizable vinyl compounds. Examples of such copolymers are1:1 styrene-glycidylmethacrylate, 1:1methylmethacrylate-glycidylacrylate, and a 62.5:24:13.5methylmethacrylate-ethyl acrylate-glycidylmethacrylate. Other usefulepoxy resins are well known and contain such epoxides asepichlorohydrins, alkylene oxides (for example, propylene oxide),styrene oxide, alkenyl oxides (for example, butadiene oxide), andglycidyl esters (for example, ethyl glycidate).

Useful epoxy-functional polymers include epoxy-functional silicones suchas those described in U.S. Pat. No. 4,279,717 (Eckberg), which arecommercially available from the General Electric Company. These arepolydimethylsiloxanes in which 1–20 mole % of the silicon atoms havebeen substituted with epoxyalkyl groups (preferably, epoxycyclohexylethyl, as described in U.S. Pat. No. 5,753,346 (Kessel)).

Blends of various epoxy-containing materials can also be utilized. Suchblends can comprise two or more weight average molecular weightdistributions of epoxy-containing compounds (such as low molecularweight (below 200), intermediate molecular weight (about 200 to 10,000),and higher molecular weight (above about 10,000)). Alternatively oradditionally, the epoxy resin can contain a blend of epoxy-containingmaterials having different chemical natures (such as aliphatic andaromatic) or functionalities (such as polar and non-polar). Othercationically-reactive polymers (such as vinyl ethers and the like) canadditionally be incorporated, if desired.

Preferred epoxy materials include monomers and/or resins having withhigh refractive index, including aromatic, mono-, di-, and higherfunctionality, including for instance aromatic glycidyl epoxies (such asphenyl glycidyl ether and the Epon™ resins available from ResolutionPerformance Products), brominated epoxies, and cycloaliphatic epoxies(such as ERL-4221 and ERL-4299 available from Union Carbide).

One or more polyols are typically provided to co-react with the epoxyfunctional material(s). Preferred polyols include those with aromaticfunctionality, including ethoxylated bisphenols,9,10-bis(2-hydroxyethyl)anthracene,9-(2-(1,3-dihydroxy)propyl)phenanthrene, and the like. See also U.S.Pat. No. 5,856,373 at col. 4, line 24 to col. 6, line 17. It ispreferred that either the epoxy and/or polyol have aromaticfunctionality, especially if such material(s) are diffusing species.

Suitable cationally-reactive species also include vinyl ether monomers,oligomers, and reactive polymers (for example, methyl vinyl ether, ethylvinyl ether, tert-butyl vinyl ether, isobutyl vinyl ether,triethyleneglycol divinyl ether (Rapi-Cure™ DVE-3, available fromInternational Specialty Products, Wayne, N.J.), trimethylolpropanetrivinyl ether (TMPTVE, available from BASF Corp., Mount Olive, N.J.),and the Vectomer™ divinyl ether resins from Allied Signal (for example,Vectomer™ 2010, Vectomer™ 2020, Vectomer™ 4010, and Vectomer™ 4020 andtheir equivalents available from other manufacturers)), and mixturesthereof. Blends (in any proportion) of one or more vinyl ether resinsand/or one or more epoxy resins can also be utilized.

Suitable photopolymerizable species also have been described, forexample, in Palazzotto et al., U.S. Pat. No. 5,545,676, column 1, line65 through column 2, line 26, and by Trout et al., U.S. Pat. No.4,963,471, column 6, line 53 through column 7, line 53. Suitablecationic-polymerizable species are described, e.g., by Oxman et al.,U.S. Pat. Nos. 5,998,495 and 6,025,406, and by Dhal, et el., U.S. Pat.No. 5,759,721.

In particularly preferred embodiments, the photopolymerizable precursorcomprises (a) 10 to 100, preferably about 90, parts by weight of atleast one of 2-(1napthoxy)ethyl (meth)acrylate, 2-(2-napthoxy)ethyl(meth)acrylate, phenoxy(meth)acrylate, and mixtures thereof per (b) 0.5to 50, preferably about 10, parts by weight of at least one oftrimethylolpropane tri(meth)acrylate (TMPTA), hexanedioldi(meth)acrylate, tetraethyleneglycol di(meth)acrylate, and mixturesthereof. The use of the multifunctional materials such as the TMPTA andthe like helps to provide dimensional stability over a wide range oftemperatures, but the amount used is desirably limited so as to maintainrefractive index contrast between the resultant optical element and itsencapsulating matrix. Fluorinated (meth)acrylates, preferablyfluorinated aromatic (meth)acrylates, such as those described in U.S.Pat. No. 6,005,137, may also be used as all or a part of the precursor.

The non-diffusing binder component incorporated into thephotopolymerizable composition provides numerous benefits. Importantly,the relatively large size of preferred embodiments of such a materialcauses its diffusion rate to be relatively low, allowing the opticalelement to be formed by multiphoton photopolymerization within a stablebackground. In addition, the non-diffusing binder component contributesto the physical and refractive index characteristics of the resultingarticle. For instance, the non-diffusing binder component helps toreduce shrinkage upon curing and improves resilience and toughness,cohesion, adhesion, flexibility, tensile strength, and the like. Bychoosing the non-diffusing binder component so that it has a lower indexof refraction in the cured (if any) and/or uncured states, opticalperformance of the optical element encapsulated in such a material canbe enhanced as well. Generally, to avoid light scattering, thenon-diffusing binder component is miscible with the photopolymerizableprecursor before and preferably after such precursor is cured. It isalso preferred that the non-diffusing binder component is at leastsubstantially non-crystalline before and preferably after the precursoris cured. Preferred materials are also solvent soluble and generallyhave a weight average molecular weight of at least about 1000,preferably 1000 to 2,000,000 or more.

The non-diffusing binder component may be thermoplastic or thermosettingor sol-based. If thermosetting, the non-diffusing binder component maybe photocurable. Alternatively, the thermosetting binder material mayinclude a different kind of curing functionality than does thephotopolymerizable precursor. Upon curing, such a material will form anIPN with the photopolymerized matrix material. If a thermoplastic isused, such a material will tend to form a semi-IPN with thephotopolymerized matrix material. In one embodiment, the non-diffusingbinder component may include pendant hydroxyl functionality. In thepresence of an isocyanate crosslinking agent and a suitable catalystsuch as dibutyl tin dilaurate, pendant hydroxyl moieties will undergourethane crosslinking reactions with the NCO groups of the isocyanatecrosslinking agent to form a crosslinked network comprising urethanelinkages.

Useful thermoplastic polymers may include acrylates and methacrylates,poly(vinyl esters), ethylene/vinyl acetate copolymers, styrenic polymersand copolymers, vinylidene chloride copolymers, vinyl chloride polymersand copolymers, cellulose esters, cellulose ethers, as described inEuropean Patent Application No. 377,182, page 6, lines 8 through 42, andin U.S. Pat. No. 4,963,471, column 5, line 6 through column 6, line 50,combinations of these, and the like.

In other embodiments, the non-diffusing binder component may be athermosetting polymer selected from epoxy resins, amine-cured epoxyresins, polyacrylates and polymethacrylates, polyurethanes,polytriazines and poly(vinyl ethers), polyesters, polyethers,polysilicones, fluoropolymers, polysulfones, polyimides, polyamides,polyamideimides, polyolefins, with the proviso that the precursors tosuch thermosetting polymer are chosen such that the resulting thermosetpolymer is substantially free of covalent bonds with themultiphotonically photopolymerized polymer matrix. More preferably, thenon-diffusing binder component comprises cellulose acetate butyrate suchas the CAB-531 material commercially available from Eastman Chemical,Kingsport, Tenn.

As used herein, “substantially non-diffusing” means that the diffusionlength over the time between imagewise exposure and blanket exposure isless than the dimensions of optical elements formed in imagewiseexposure. Advantageously, this allows the binder to provide a stablebackground within which to form three-dimensional elements.

The amount of the non-diffusing binder component used may vary within awide range. Preferably, using 25 to 75 parts by weight of thenon-diffusing binder component per 5 to 60 parts by weight of thephotopolymerizable precursor would be suitable in the practice of thepresent invention.

The multiphoton photoinitiator system of the present inventionpreferably includes at least one multiphoton photosensitizer and atleast one photoinitiator that is capable of being photosensitized by thephotosensitizer, more preferably additionally including at least oneelectron donor. While not wishing to be bound by theory, it is believedthat light of sufficient intensity and appropriate wavelength to effectmultiphoton absorption can cause the multiphoton photosensitizer to bein an electronic excited state via absorption of two photons, whereassuch light is generally not capable of directly causing the photocurablematerials to be in an electronic excited state by one photon absorption.The photosensitizer is believed to then transfer an electron to thephotoinitiator, causing the photoinitiator to be reduced. The reducedphotoinitiator can then cause the photocurable materials to undergo thedesired curing reactions. As used herein, “cure” means to effectpolymerization and/or to effect crosslinking. Thus, by appropriatefocusing of such light, photocuring can be controllably induced in thevolume of focus with relatively high resolution to form optical elementswith simple or complex, three dimensional geometry, as desired.

Multiphoton photosensitizers are known in the art and illustrativeexamples having relatively large multiphoton absorption cross-sectionshave generally been described e.g., by Marder, Perry et al., in PCTPatent Applications WO 98/21521 and WO 99/53242, and by Goodman et al.,in PCT Patent Application WO 99/54784. Although multiphotoncross-sections greater than fluorescein are not necessary for carryingout the present invention, in preferred aspects of the presentinvention, multiphoton photosensitizers suitable for use in themultiphoton photoinitiator system of the photoreactive compositions arethose that are capable of simultaneously adsorbing at least two photonswhen exposed to sufficient light and that have a two-photon absorptioncross-section greater than that of fluorescein (that is, greater thanthat of 3′,6′-dihydroxyspiro[isobenzofuran-1(3H), 9′-[9H]xanthen]3-one).Generally, the cross-section can be greater than about 50×10⁻⁵⁰ cm⁴sec/photon, as measured by the method described by C. Xu and W. W. Webbin J. Opt. Soc. Am. B. 13, 481 (1996) (which is referenced by Marder andPerry et al. in International Publication No. WO 98/21521 at page 85,lines 18–22).

This method involves the comparison (under identical excitationintensity and photosensitizer concentration conditions) of thetwo-photon fluorescence intensity of the photosensitizer with that of areference compound. The reference compound can be selected to match asclosely as possible the spectral range covered by the photosensitizerabsorption and fluorescence. In one possible experimental set-up, anexcitation beam can be split into two arms, with 50% of the excitationintensity going to the photosensitizer and 50% to the referencecompound. The relative fluorescence intensity of the photosensitizerwith respect to the reference compound can then be measured using twophotomultiplier tubes or other calibrated detector. Finally, thefluorescence quantum efficiency of both compounds can be measured underone-photon excitation.

Assuming that the emitting state is the same under one- and two-photonexcitation (a common assumption), the two-photon absorptioncross-section of the photosensitizer, (δ_(sam)), is equal toδ_(ref)(I_(sam)/I_(ref))(Φ_(sam/Φ) _(ref)), wherein δ_(ref) is thetwo-photon absorption cross-section of the reference compound, I_(sam)is the fluorescence intensity of the photosensitizer, I_(ref) is thefluorescence intensity of the reference compound, Φ_(sam) is thefluoroescence quantum efficiency of the photosensitizer, and Φ_(ref) isthe fluorescence quantum efficiency of the reference compound. To ensurea valid measurement, the clear quadratic dependence of the two-photonfluorescence intensity on excitation power can be confirmed, andrelatively low concentrations of both the photosensitizer and thereference compound can be utilized (to avoid fluorescence reabsorptionand photosensitizer aggregation effects).

Although not necessary for carrying out the present invention, it ispreferred that the two-photon absorption cross-section of thephotosensitizer is greater than about 1.5 times that of fluorescein (or,alternatively, greater than about 75×10⁻⁵⁰ cm⁴ sec/photon, as measuredby the above method); more preferably, greater than about twice that offluorescein (or, alternatively, greater than about 100×10⁻⁵⁰ cm⁴sec/photon); most preferably, greater than about three times that offluorescein (or, alternatively, greater than about 150×10⁻⁵⁰ cm⁴sec/photon); and optimally, greater than about four times that offluorescein (or, alternatively, greater than about 200×10⁻⁵⁰ cm⁴sec/photon).

Preferably, the photosensitizer is soluble in the photocurable materialsused to form body 20 of the composition. Most preferably, thephotosensitizer is also capable of sensitizing2-methyl-4,6-bis(trichloromethyl)-s-triazine under continuousirradiation in a wavelength range that overlaps the single photonabsorption spectrum of the photosensitizer (single photon absorptionconditions), using the test procedure described in U.S. Pat. No.3,729,313. Using currently available materials, that test can be carriedout as follows:

A standard test solution can be prepared having the followingcomposition: 5.0 parts of a 5% (weight by volume) solution in methanolof 45,000–55,000 molecular weight, 9.0–13.0% hydroxyl content polyvinylbutyral (Butvar™ B76, Monsanto); 0.3 parts trimethylolpropanetrimethacrylate; and 0.03 parts2-methyl-4,6-bis(trichloromethyl)-s-triazine (see Bull. Chem. Soc.Japan, 42, 2924–2930 (1969)). To this solution can be added 0.01 partsof the compound to be tested as a photosensitizer. The resultingsolution can then be knife-coated onto a 0.05 mm clear polyester filmusing a knife orifice of 0.05 mm, and the coating can be air dried forabout 30 minutes. A 0.05 mm clear polyester cover film car be carefullyplaced over the dried but soft and tacky coating with minimum entrapmentof air. The resulting sandwich construction can then be exposed forthree minutes to 161,000 Lux of incident light from a tungsten lightsource providing light in both the visible and ultraviolet range (FCH™650 watt quartz-iodine lamp, General Electric). Exposure can be madethrough a stencil so as to provide exposed and unexposed areas in theconstruction. After exposure the cover film can be removed, and thecoating can be treated with a finely divided colored powder, such as acolor toner powder of the type conventionally used in xerography. If thetested compound is a photosensitizer, the trimethylolpropanetrimethacrylate monomer will be polymerized in the light-exposed areasby the light-generated free radicals from the2-methyl-4,6-bis(trichloromethyl)-s-triazine. Since the polymerizedareas will be essentially tack-free, the colored powder will selectivelyadhere essentially only to the tacky, unexposed areas of the coating,providing a visual image corresponding to that in the stencil.

Preferably, a multiphoton photosensitizer can also be selected based inpart upon shelf stability considerations. Accordingly, selection of aparticular photosensitizer can depend to some extent upon the particularreactive species utilized (as well as upon the choices of electron donorcompound and/or photoinitiator, if either of these are used).

Particularly preferred multiphoton photosensitizers include thoseexhibiting large multiphoton absorption cross-sections, such asRhodamine B (that is,N-[9-(2-carboxyphenyl)-6-(diethylamino)-3H-xanthen-3-ylidene]-N-ethylethanaminiumchloride) and the four classes of photosensitizers described, forexample, by Marder and Perry et al. in International Patent PublicationNos. WO 98/21521 and WO 99/53242. The four classes can be described asfollows: (a) molecules in which two donors are connected to a conjugatedπ (pi)-electron bridge; (b) molecules in which two donors are connectedto a conjugated π (pi)-electron bridge which is substituted with one ormore electron accepting groups; (c) molecules in which two acceptors areconnected to a conjugated π (pi)-electron bridge; and (d) molecules inwhich two acceptors are connected to a conjugated π (pi)-electron bridgewhich is substituted with one or more electron donating groups (where“bridge” means a molecular fragment that connects two or more chemicalgroups, “donor” means an atom or group of atoms with a low ionizationpotential that can be bonded to a conjugated π (pi)-electron bridge, and“acceptor” means an atom or group of atoms with a high electron affinitythat can be bonded to a conjugated π (pi)-electron bridge). The fourabove-described classes of photosensitizers can be prepared by reactingaldehydes with ylides under standard Wittig conditions or by using theMcMurray reaction, as detailed in International Patent Publication No.WO 98/21521.

Other multiphoton photosensitizer compounds are described by Reinhardtet al. (for example, in U.S. Pat. Nos. 6,100,405, 5,859,251, and5,770,737) as having large multiphoton absorption cross-sections,although these cross-sections were determined by a method other thanthat described herein. Other suitable multiphoton initiators also havealso been described in Goodman, et al in PCT Patent Publication WO99/54784, Mukesh P. Joshi et al., “Three-dimensional optical circuitryusing two-photo-assisted polymerization,” Applied Physics Letters,Volume 74, Number 2, Jan. 11, 1999, pp. 170–172; Cornelius Diamond etal., “Two-photon holography in 3-D photopolymer host-guest matrix,”OPTICS EXPRESS, Vol. 6, No. 3, Jan. 31, 2000, pp. 64–68; Brian H.Cumpston et al., “Two-photon polymerization initiators forthree-dimensional optical data storage and microfabrication,” NATURE,Vol. 398, Mar. 4, 1999, pp. 51–54; T. J. Bunning et al., “ElectricallySwitchable Gratings Formed Using Ultrafast HolographicTwo-Photon-Induced Photopolymerization,” Chem. Mater. 2000, 12,2842–2844; Cornelius Diamond et al., “Two-photon holography in 3-Dphotopolymer host-guest matrix: errata,” OPTICS EXPRESS, Vol. 6, No. 4,Feb. 14, 2000, pp. 109–110; S. M. Kirkpatrick et al., “Holographicrecording using two-photon-induced photopolymerization,” Appl. Phys. A69, 461–464 (1999); Hong-Bo Sun et al., “Three-dimensional photoniccrystal structures achieved with two-photon-absorptionphotopolymerization of material,” APPLIED PHYSICS LETTERS, Volume 74,Number 6, Feb. 8, 1999, pp. 786–788; and Kevin D. Belfield et al.,“Near-IR Two-Photon Photoinitiated Polymerization Using a Fluorone/AmineInitiating System,” J. Am. Chem. Soc. 2000, 122, 1217–1218.

The preferred multiphoton photoinitiator system generally includes anamount of the multiphoton photosensitizer that is effective tofacilitate photopolymerization within the focal region of the energybeing used for imagewise curing. Using from about 0.01 to about 10,preferably 0.1 to 5, parts by weight of the multiphoton initiator per100 parts by weight of the photocurable material(s) would be suitable inthe practice of the present invention.

In addition to the multiphoton photosensitizer, the preferredmultiphoton photoinitiator system of the present invention may includeother components that help to enhance the performance of photocuring.For instance, certain one-photon photoinitiators can be photosensitizedby the multiphoton photosensitizer and, consequently, function aselectron mediators in multiphoton photocuring reactions. One or moreelectron donor compounds optionally may be included in the multiphotonphotoinitiator system. Multiphoton photoinitiator systems comprisingone-photon photoinitiators and/or electron donor compounds are describedin Assignee's co-pending application titled MULTIPHOTONPHOTOSENSITIZATION SYSTEM, filed concurrently herewith on Jun. 14, 2001,in the name of Robert J. DeVoe, application Ser. No. 10/311,041, theentirety of which is incorporated herein by reference.

One-photon photoinitiators useful in the present invention include oniumsalts, such as sulfonium, diazonium, azinium, and iodonium salts such asa diaryliodonium salt, chloromethylated triazines, such as2-methyl-4,6-bis(trichloromethyl)-s-triazine, and triphenylimidazolyldimers. Useful iodonium salts are those that are capable of initiatingpolymerization following one-electron reduction or those that decomposeto form a polyrnerization-initiating species. Suitable iodonium saltsare described by Palazzotto et al., in U.S. Pat. No. 5,545,676, incolumn 2, lines 28 through 46. Useful chloromethylated triazines includethose described in U.S. Pat. No. 3,779,778, column 8, lines 45–50.Useful triphenylimidazolyl dimers include those described in U.S. Pat.No. 4,963,471, column 8, lines 18–28, the teachings of which areincorporated herein by reference. These dimers include, for example,2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)imidazole dimer.

As described in Assignee's co-pending application titled MULTIPHOTONPHOTOSENSITIZATION SYSTEM, filed concurrently herewith on Jun. 14, 2001,in the name of Robert J. DeVoe, application Ser. No. 10/311,041, suchother components also may include both an electron donor compound and aphotoinitiator. Advantageously, use of this combination enhances thespeed and resolution of multiphoton curing. The photoinitiator servesdouble duty, as well, by also optionally facilitating blanketphotodefining of the photodefinable composition with suitable curingenergy. When such an electron donor and/or single photon initiator areused, the composition may include up to about 10, preferably 0.1 to 10,parts by weight of one or more electron donors and 0.1 to 10, preferably0.1 to 5, parts by weight of one or more single photon initiators per 5to 100 parts by weight of the multiphoton initiator.

A wide variety of optional adjuvants may also be included in thephotopolymerizable compositions of the present invention, depending uponthe desired end use. Suitable adjuvants include solvents,diluentsplasticizers, pigments, dyes, inorganic or organic reinforcingor extending fillers, thixotropic agents, indicators, inhibitors,stabilizers, ultraviolet absorbers, medicaments (for example, leachablefluorides), and the like, but should be chosen so as not to undulyadversely affect the optical properties of the resultant opticalelements. The amounts and types of such adjuvants and their manner ofaddition to the compositions will be familiar to those skilled in theart.

The photopolymerizable compositions of the present invention can beprepared by any suitable method in accordance with conventionalpractices. In one approach, the components are combined under “safelight” conditions using any order and manner of combination (optionally,with stirring or agitation), although it is sometimes preferable (from ashelf life and thermal stability standpoint) to add thephotoinitiator(s) last (and after any heating step that is optionallyused to facilitate dissolution of other components). Solvent can beused, if desired, provided that the solvent is chosen so as to not reactappreciably with the components of the composition. Suitable solventsinclude, for example, acetone, dichloromethane and other halogenated(preferably chlorinated) hydrocarbons, and acetonitrile. The monomericconstituents of the photopolymerizable precursor sometimes serve as asolvent for the other components.

FIG. 5 schematically illustrate a preferred mode of implementing thepresent invention in which a device 100 of the present inventionincorporating a partially completed encapsulated optical element in theform of waveguide 101 is completed in situ to optically couple theelement 101 to another optical device 102. The first device 100 isbutted against the second optical device 102. Waveguide 101 is partiallycompleted in the sense that end 104 of waveguide 101 does not fullyextend to boundary 106. Waveguide 101 is surrounded by encapsulatingmaterial 108. Material 108 is photocurable, and preferably includesphotocurable material and a multiphoton photoinitiator system asdescribed herein, allowing material 108 to be imagewise photocured viamultiphoton polymerization techniques and/or via blanket irradiationtechniques. Thus, a region 110 of such photocurable material ispositioned between end 104 and boundary 106.

Second optical device 102, for purposes of illustration includes glassfiber core 112 surrounded by cladding 114. A protective layer 116, inturn, surrounds cladding 114. An end 118 of glass fiber core 112 is atleast in substantial alignment with end 104 of waveguide 101. In thepractice of the invention, precise alignment between ends 104 and 118 isnot required to achieve effective coupling between waveguide 101 andglass fiber core 112. For example, it is possible for the longitudinalaxes of waveguide 101 and core 112 to be slightly out of alignment withrespect to each other by up to a few degrees or less, preferably 1degree or less, more preferably 0.1 degree or less. Additionally, ends104 and 118 also may be offset from each other. The ability to coupleelements together with relaxed tolerances is a tremendous advantage ofthe present invention. In contrast, conventional coupling processesrequire much greater precision when two optical elements are to bejoined to each other.

In the practice of the invention, region 110 will be photocured in situto finish waveguide 101 and thereby couple waveguide 101 and fiber core112 together. The width of region 110 can vary within a wide range whilestill allowing such in situ curing to be carried out. As suggestedguidelines, the width of region 110 between waveguide 101 and fiber core112 may range from a few nanometer to a few millimeters, morepreferably, 50 nm to 500 micrometers, most preferably about 50 nm toabout 0.2 micrometers.

FIG. 5 shows one manner by which in situ curing of first element 100 canbe carried out with relative ease. Light of suitable wavelength (e.g.,matching the wavelength of light that may be guided by waveguide 101and/or glass fiber core 112) and intensity to cause multiphotonpolymerization is caused to enter waveguide 101, glass fiber core 112,or both. As shown in FIG. 5, laser light pulses 122 and 124 areintroduced through both waveguide 101 and core 112 towards region 110.At least some of such light will be guided by waveguide 101 and fibercore 112, respectively, and be transmitted through region 110. As aconsequence, portions of region 110 will absorb the light and bephotocured as a consequence. Waveguide 101 is thus completed and becomesoptically coupled to glass fiber core 112. After waveguide 101 has beencompleted and coupled to fiber core 112 in situ in this manner, firstoptical device 100 may be subjected to suitable blanket irradiation tophotocure matrix material 108 and form a protective encapsulating matrixat least around waveguide 101.

The process depicted in FIG. 5 has many advantages. First, as notedabove, the method provides an alignment advantage in that the twooptical devices 100 and 102 need not be precisely aligned in order foreffective coupling to be carried out. Second, because material 108 isnot fully cured when the two devices are butted against each other, thepresent invention reduces the need to polish the butted faces of device100 and/or 102 before the two devices are butted together. Thiseliminates the need for the polishing step in the manufacturing process,helping to make the process economical and reducing cycle time. Third,because alignment tolerances are more relaxed, insertion losses arereduced.

In FIG. 5, only device 100 incorporates the partially completedwaveguide 101, while device 102 is completed. However, the methodologyof FIG. 5 may also be used to couple two devices together in which eachincludes at least one light guiding portion (comparable to region 108 ofFIG. 5) that will be completed in situ after the two devices arepositioned together.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

EXAMPLE 1

A solution (40% solids in methylene chloride) containing 40% by weightpolymethyl methacrylate (mw 120,000, n=1.490, Aldrich Chemical Co.,Milwaukee, Wis.), 25% by weight phenoxyethyl acrylate, 34% by weight ofbisphenol A glycerolate diacrylate (Ebecryl 3700™, UCB Chemicals,Symrna, Ga.), and 1% by weight 4,4′-bis(diphenylamino)-trans-stilbene isprepared. The solution is coated on a silicon wafer approximately 500microns thick and dried in an oven at 60° C. Exposure is performed usinga two-photon microscope with a Ti:Sapphire laser operating thetwo-photon absorption maximum of 4,4′-bis(diphenylamino)-trans-stilbene,700 nm, and the light is focused through an oil-immersion objective withNA=1.4. X-Y-Z control of the sample is accomplished using a manipulatormounted on the microscope stage. A pattern of interconnected waveguideswith primary axes parallel and perpendicular to the plane of the film iswritten into the medium, resulting in a three dimensional image of thepattern, wherein the refractive index modulation of the cured waveguidesis at least 0.01 relative to the subsequently-cured matrix. The coatingis then blanket-exposed in a non-imagewise manner using a bank of 6Sylvania F15T8/350BL bulbs with primary output at 350 nm (OsramSylvania, Inc., Danvers, Mass.) for 10 minutes. The film maintains arefractive index modulation of at least 0.01 relative to the waveguides,with the waveguides capable of effectively carrying injected light.

EXAMPLE 2

A solution (40% solids in methylene chloride) containing 60% by weightcellulose acetate butyrate (MW 70,000, 13.5 wt % acetyl, 37 wt %butyryl, Aldrich Chemical Co., Milwaukee, Wis.), 25% by weightphenoxyethyl acrylate (Aldrich Chemical Co.), 34% by weight bisphenol Aglycerolate diacrylate (Ebecryl 3700™, UCB Chemicals), and 1% by weight4,4′-bis(diphenylamino)-trans-stilbene is prepared. The solution iscoated on a silicon wafer approximately 500 microns thick and dried inan oven at 60° C. Exposure is performed using a two-photon microscopewith a Ti:Sapphire laser operating at the two-photon absorption maximumof 4,4′-bis(diphenylamino)-trans-stilbene, 700 nm, and the light isfocused through an oil-immersion objective with NA=1.4. X-Y-Z control ofthe sample is accomplished using a manipulator mounted on the microscopestage. A pattern of interconnected waveguides with primary axes paralleland perpendicular to the plane of the film is written into the medium,resulting in a three dimensional image of the pattern, wherein therefractive index modulation is at least 0.01. The coating is thenblanket-exposed in a non-imagewise manner using a bank of 6 SylvaniaF15T8/350BL bulbs having a primary output at 350 nm (Osram Sylvania,Inc.) for 10 minutes. The film maintains a refractive index modulationof at least 0.01 relative to the waveguides, with the waveguides capableof effectively carrying injected light.

MATERIALS USED IN EXAMPLES 3–5

Unless otherwise noted, chemicals used in the examples 3–5 werecommercially available from Aldrich Chemical Co., Milwaukee, Wis. CGI7460 was a borate salt that was commercially available from CibaSpecialty Chemicals, Tarrytown, N.Y., and CD1012 is a diaryliodoniumhexafluoroantimonate salt that was commercially available from SartomerCompany, West Chester, Pa. The material 2-(1-Naphthoxy)ethyl acrylatewas made in accordance with the procedure described prior to Example 1at page 13 of assignee's co-ending application Ser. No. 09/746,613,filed Dec. 21, 2000.

The two-photon sensitizing dye,Bis-[4-(diphenylamino)stryl]-1,4-(dimethoxy)benzene was prepared asfollows:

(1) Reaction of 1,4-bis-bromomethyl-2,5-dimethoxybenzene with TriethylPhosphite: 1,4-bis-bromomethyl-2,5-dimethoxybenzene was preparedaccording to the literature procedure (Syper et. al., Tetrahedron, 1983,39, 781–792). 1,4-bis-bromomethyl-2,5-dimethoxybenzene (253 g, 0.78 mol)was placed into a 1000 mL round bottom flask. Triethyl phosphite,P(OEt)₃, (300 g, 2.10 mol) was added. The reaction was heated tovigorous reflux with stirring for 48 hours under nitrogen atmosphere.The reaction mixture was cooled and the excess P(OEt)₃ was removed undervacuum using a Kugelrohr apparatus. The desired product was not actuallydistilled, but a Kugelrohr apparatus was used to remove the excessP(OEt)₃ by distilling it away from the product. Upon heating to 100° C.at 0.1 mmHg, a clear oil resulted. Upon cooling, the desired productsolidified. The product was suitable for use directly in the next step,and ¹H NMR was consistent with the proposed structure:

Re-crystallization from toluene yielded colorless needles and resultedin a purer product, but this was not necessary for subsequent steps inmost cases.

(2) Synthesis of Bis-[4-(diphenylamino)stryl]-1,4-(dimethoxy)benzene: A1000 mL round bottom flask was fitted with a calibrated dropping funneland a magnetic stirrer. The flask was charged with the Horner Eamonsreagent as prepared above (19.8 g, 45.2 mal), and it was also chargedwith N,N-diphenylamino-p-benzaldehyde (Fluka, 25 g, 91.5 mmol). Theflask was flushed with nitrogen and sealed with septa. Anhydroustetrahydrofuran (750 mL) was cannulated into the flask and all solidsdissolved. The dropping funnel was charged with KOtBu (Potassiumtert-butoxide) (125 mL, 1.0 M in THF). The solution in the flask wasstirred and the KOtBu solution was added to the contents of the flaskover the course of 30 minutes. The solution was then left to stir atambient temperature overnight. The reaction was then quenched by theaddition of H₂O (500 mL). The reaction continued to stir and after about30 minutes a highly fluorescent yellow solid had formed in the flask.The solid was isolated by filtration and air-dried. It was thenre-crystallized from toluene (450 mL). The desired product was obtainedas fluorescent needles (24.7 g, 81% yield). ¹H NMR was consistent withthe proposed structure:

EXAMPLE 3

A low refractive index buffer layer between glass and active layers wasprepared by spin coating a solution of the composition given in Table 1(16% solids in 1,2-dichloroethane) onto microscope slides, evaporatingthe solvent in an 80° C. oven for 10 minutes, and then curing for 10minutes under Sylvania 350BLB UV lights. The cured buffer layerthickness was approximately 10 microns thick.

TABLE 1 Composition of the buffer layer Ingredient Weight % Celluloseacetate butyrate (Eastman Chemicals, 89.37 Kingsport, TN)Trimethylpropane triacrylate, SR-351 (Sartomer Co. 8.94 West Chester,PA) Benzil dimethyl ketal, Esacure KB1 (Sartomer Co. 1.70 West Chester,PA)The active layer, the composition of which is given in Table 2, was thenspun coat from 25% solids solution in 1,2-dichloroethane on top of theprepared buffer layer and dried in an 80° C. oven for 10 minutes. Tofurther increase the thickness, a second active layer was spun on topand the samples dried again. The final thickness of the curable coating,including buffer layer was approximately 65 microns. All samplepreparation was done under safe lights. The dried samples were stored ina light-tight box prior to exposure.

TABLE 2 Composition of the active layer Ingredient Weight % Celluloseacetate butyrate (Eastman Chemicals, 50.71 Kingsport, TN) 2-phenoxyethylacrylate, SR339 (Sartomer Co. 37.48 West Chester, PA)2-(1-Naphthoxy)ethyl acrylate 6.25 Trimethylpropane triacrylate, SR-351(Sartomer Co. 0.89 West Chester, PA)Bis-[4-(diphenylamino)stryl]-1,4-(dimethoxy)benzene 0.93 CGI 7460 (CibaSpecialty Chemicals, Tarrytown, NY) 1.87 CD1012 (Sartomer Co. WestChester, PA) 1.87

Exposure of the curable composition covered substrate occurred bycontinuously moving the sample beneath a highly focused light from amicroscope objective. The focal position of the beam was positionedbelow the surface of the curable composition. The light source was adiode pumped Ti:sapphire laser (Spectra-Physics) operating at awavelength of 800 nm, pulse width 100 fs, pulse repetition rate of 80MHz, beam diameter of approximately 2 mm. The optical train included lowdispersion turning mirrors, an optical attenuator to vary the opticalpower, and a 40× microscope objective to focus the light into thesample. In all cases the average power delivered to the sample (98 mW)was measured where the beam exited the microscope objective using aCoherent Power Meter. The substrate was moved underneath the focussedbeam using a computer controlled, 3-axis stage. A pattern of waveguidesand splitters was written into the medium. The coating was thenblanket-exposed in a non-image wise manner using a bank of 3 PhillipsTLD 15W-03 bulbs for 45 minutes.

For waveguide optical mode and loss measurements, a glass microscopeslide was bonded on top of the device using OG125 low refractive indexepoxy (EPO-TEK, Billerica, Mass.). The sample was then diced using a diesaw to expose the ends of the waveguides. A 9 micrometer core diametertelecommunications optical fiber was aligned with one of the waveguidesand positioned to provide a maximum light intensity at the output endusing a 3-axis micropositioner. 1550 nm wavelength light was introducedinto the polished input ends of the waveguide using a ILX Lightwave 7000system, precision fiber optic source. The near field light distributionwas imaged using 5× microscope objective and an infrared camera. Theimages showed that the waveguide supported 2 TE modes at 1550 nm. When657 nm light was input into the waveguide, the waveguide showedmultimode behavior.

For loss measurements, the transmitted light was directed onto a HewlettPackard GMGH germanium photodetector and the transmitted power measured.The input power was determined immediately after the measurement byremoving the sample and positioning the input fiber where the output endof the waveguide had been, thereby capturing the input reference powerwith the same optical path and equipment by which the transmitted lightpower had been determined. Input power levels were about 30 to 100microwatts, depending on the source. The loss at 1550 nm was measured asapproximately 5.4 dB/cm. The losses increased with decreasingwavelength.

EXAMPLE 4

In this example, the dose of curing energy received by the samples wasvaried in order to control the refractive index contrast. A sample ofthe same composition as described in Tables 1 and 2 was prepared andexposed using a 60× microscope objective (N.A. in air is 0.85) and anaverage power of 106 mW. The sample was positioned so that the focalpoint of the beam was approximately in the middle of the curable layer.Waveguides were created by scanning the sample under the focussed beamat speeds from ranging from 50 micrometers/s to 51.2 mm/s. The coatingwas then blanket-exposed in a non-image wise manner using a bank of 3Phillips TLD 15W-03 bulbs for 45 minutes. The refractive index of eachwaveguide was determined using Mach Zehnder interferometry on a JenaInterference microscope with white light. The refractive index of thebulk film was determined to be 1.49 using the Jena Interferometer. Thedata showed that the refractive index contrast in the waveguideincreased with the log of increasing dose substantially linearly from acontrast of about 0.002 at −4.5 (log dose, J/micrometer) to about 0.063at −2.8 (log dose, J/micrometer). The dose was determined by the averagepower divided by the linear scan speed and has units of Joules permicron. Over this energy range there was no evidence of sample damage.

EXAMPLE 5

In this example, waveguides and Y-splitters are demonstrated. A sampleof the same composition as described in Tables 1 and 2 was prepared andexposed using a 40× microscope objective (N.A. in air is 0.65) and anaverage power of 60 mW. A 10 cm focal length field lens was placed inthe optical train in order to expand the beam to fill the full apertureof the microscope objective. The Y-splitter was written by making 5passes at 20 mm/s over the same pattern. Optical micrographs were usedto observe the splitter viewed from the top and in cross-section. Thesplitter was clearly encapsulated within the bulk of the material, andthe lateral width of each arm was about 2 micrometers. In cross-section,the structure included, in order from the top, a glass layer, a layer ofthe treated composition, an epoxy layer, and another glass layer. Forthe cross-section image, a glass slide was bonded to the top surface asdescribed in example 3 and the sample diced to expose the ends of thewaveguide.

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

1. A method of fabricating an encapsulated optical element, said methodcomprising the steps of: (a) providing a body comprising: (i) aphotopolymerizable precursor comprising a diffusing species, saidprecursor forming a polymer matrix upon photopolymerization, and saidpolymer matrix having an index of refraction; (ii) a substantiallynon-diffusing binder component having an index of refraction that islower than the index of refraction of the polymer matrix and that ismiscible with the photopolymerizable precursor; and (iii) a multiphotonphotoinitiator system; (b) imagewise exposing at least a portion of thebody to energy under conditions effective to multiphoton photopolymerizethe polymer precursor in a pattern effective to form a three-dimensionaloptical element; and (c) after imagewise exposing the body; nonimagewiseexposing at least a portion of the body to a photopolymerizing fluenceof energy.
 2. The method of claim 1, wherein the binder is derived fromingredients comprising a thermoplastic polymer.
 3. The method of claim1, wherein the binder is derived from ingredients comprising athermosetting polymer having substantially no photocurablefunctionality.
 4. The method of claim 1, wherein the multiphotonphotoinitiator system comprises a multiphoton photosensitizer.
 5. Themethod of claim 4, wherein the multiphoton photoinitiator system furthercomprises a single photon photoinitiator.
 6. The method of claim 5,wherein the multiphoton photoinitiator system further comprises anelectron donor.
 7. The method of claim 1, wherein the nonimagewiseexposing step comprises causing single photon polymerization.
 8. Themethod of claim 1, wherein the nonimagewise exposing step comprisescausing multiphoton polymerization.
 9. The method of claim 1 wherein theimagewise exposing step comprises causing a depletion zone to be formedat a boundary of the optical element, said depletion zone comprising areduced amount of the diffusing species.
 10. The method of claim 1,wherein the imagewise exposing step comprises causing a plurality offemtosecond laser pulses to be directed into the body.
 11. The method ofclaim 1 wherein said body comprises a homogeneous admixture ofingredients comprising said precursor and said binder.
 12. The method ofclaim 1, wherein said optical element is a waveguide.
 13. The method ofclaim 1, wherein said imagewise exposure step occursnon-holographically.
 14. The method of claim 1, wherein the precursorcomprises at least one aromatic (meth)acrylate monomer.
 15. The methodof claim 1, wherein the precursor comprises at least one aromatic,(meth)acrylate comprising a fluorinated moiety.
 16. The method of claim1, wherein the precursor comprises 10 to 100 parts by weight of at leastone of 2-(1-napthoxy)ethyl(meth)acrylate, 2-(2-napthoxy)ethyl(meth)acrylate, phenoxy(meth)acrylate, and mixtures thereof per (b) 0.5to 50 parts by weight of at least one multifunctional (meth)acrylatemonomer.
 17. The method of claim 1, wherein the multifunctional(meth)acrylate monomer comprises at least one of trimethylolpropanetri(meth)acrylate (TMPTA), hexanediol di(meth)acrylate,tetraethyleneglycol di(meth)acrylate, and mixtures thereof.